Biochemical characterization of a cefotaximehydrolysing &#946-lactamase encoded by a conjugative plasmid

During the nosocomials infections occurring in the intensive care unit of the military hospital of Tunis in 2005, the Enterobacter cloacae BW 1150 strain was isolated from a stool culture. This strain was found to have a high level resistance to broad-spectrum -lactams. Resistance profile against thevarious families of antibiotics was determined using the disc diffusion test. The minimal inhibitory concentrations values showed that this strain was resistant to the -lactams such as ampicillin and the extended spectrum cephalosporins (cefotaxime, ceftriaxon and cefpirome). Analysis of this strain by the disk diffusion test revealed synergies between amoxicillin-clavulanate (AMX-CA) and ceftriaxon, ceftazidime and cefotaxime. Cell sonicate of this isolate is very active against cefotaxime and showed aspecific activity (AS) of 7.54 U/mg for the same antibiotic. This activity was inhibited by the sulbactam and the clavulanic acid. Isoelectrofocusing methods revealed that the crude extract of the E. cloacae BW 1150 strain showed 1 - lactamase activity with an isoelectric piont (pI) of about 8. This activity was transferred by conjugation and was highly expressed in the transconjugant

Comparaison de la composition physicochimique du lait camelin et bovin du Sud tunisien; variation du pH et de l’acidité à différentes températures

La composition physicochimique du lait de chamelle est variable selon l’alimentation des animaux, les conditions environnementales ainsi que la période de lactation. Dans le but de déterminer la composition du lait de chamelle du sud tunisien, le lait camelin de la région a été comparé à celui bovin sur le plan de l’acidité et du pH du lait des deux espèces en fonction de la température du milieu. Le lait de chamelle est plus acide (17,25 ± 1,035°D) et moins dense (d= 1,027± 0,003) que le lait de vache. Le lait de vache est plus riche en matière protéique (34,15 ± 3,11 g/L), matière sèche (119,43 ± 15,34g/L) et azote non protéique NPN (1,04 ± 0,08g/L). Le suivi de la variation du pH et de l’acidité du lait camelin et bovin à trois températures différentes (température ambiante (25°C), à 4°C et à -4°C) a révélé une acidification plus lente du lait de chamelle dans les trois cas avec une conservation durant 30 heures à température ambiante, 7 jours dans le réfrigérateur (4°C) alors quelle est de 5 jours pour le lait de vache à la même température. La congélation du lait à -4°C peut ainsi constituer une méthode simple pour la conservation du lait camelin qui n’est accessible que dans les régions de sa production.Mots-clés : Lait, chamelle, vache, composition physicochimique, acidité,températur

Efficient dynamical nuclear polarization in quantum dots: Temperature dependence

We investigate in micro-photoluminescence experiments the dynamical nuclear polarization in individual InGaAs quantum dots. Experiments carried out in an applied magnetic field of 2T show that the nuclear polarization achieved through the optical pumping of electron spins is increasing with the sample temperature between 2K and 55K, reaching a maximum of about 50%. Analysing the dependence of the Overhauser shift on the spin polarization of the optically injected electron as a function of temperature enables us to identify the main reasons for this increase.Comment: 5 pages, 3 figure

CO2 laser beam welding of AM60 magnesium-based alloy

The authors are grateful to FONDERIE MESSIER HONSEL group that provided the as-cast magnesium alloy workpieces. The authors would like also to acknowledge the technical support of Dr. Moraru of the LSIS Laboratory-Arts et Métiers ParisTech-Aix En Provence-France.Magnesium alloys have a 33% lower density than aluminum alloys, whereas they exhibit the same mechanical characteristics. Their application increases in many economic sectors, in particular, in aeronautic and automotive industries. Nevertheless, their assembly with welding techniques still remains to be developed. In this paper, we present a CO2 laser welding investigation of AM60 magnesium-based alloy. Welding parameters range is determinate for the joining of 3 mm thickness sheets. The effects of process parameters including beam power, welding speed, focusing position, and shielding gas flow are studied. Experimental results show that the main parameters that determine the weld quality are the laser beam power, the welding speed, and the shielding gas flow. The focal point position has a minor effect on weld quality, however, it has an influence on melting zone width. For optimized welding parameters, metallurgical observations show that after laser welding of AM60 alloy dendritic microstructure is observed on melting zone after high solidification rate. A small heat affected zone is also detected. Finally, hardness tests indicate that microhardness of the weld is higher than that of base metal

Évaluation des niveaux d’exposition et des effets sur la santé des travailleurs exposés aux poussières de bois dans la région de Sidi-Bel-Abbès en Algérie

ObjectifL’objectif de notre enquête est d’évaluer les risques et les niveaux d’exposition aux poussières de bois inhalables chez les travailleurs du bois. Méthode Une enquête descriptive de type transversal a été menée sur une période de sept mois allant de novembre 2007 à mai 2008, auprès des 100 menuiseries recensées au niveau de la wilaya de Sidi-Bel-Abbès. Seulement 87 entreprises ont répondu positivement à notre enquête, dont l’effectif total est de 620 menuisiers. La population étudiée est constituée de 400 artisans menuisiers, exclusivement de sexe masculin répondant au critère majeur d’inclusion à savoir ayant plus de 70 % de leurs temps annuels de travail en atelier. Les menuisiers en pose seule ainsi que les apprentis ont été exclus de notre étude. Un questionnaire médical pour chaque salarié et un questionnaire technique au niveau de chaque entreprise ont été remplis par le même médecin du travail chargé de l’enquête, cela nous a permis une meilleure connaissance des pratiques de ces salariés et d’établir un score d’exposition. La saisie et l’analyse des données ont été faites avec SPSS.11.5. Résultats Un risque collectif moyen a été évalué par le calcul des scores par entreprise. Les entreprises ont été classées en trois catégories de risque : fort–moyen–faible. L’âge moyen était de 39,11 ± 1,19 ans, l’ancienneté moyenne au poste est de 17,75 ± 0,98 ans. Les fumeurs représentaient 33,3 % de notre population dont 38,34 % supérieurs à 10 PA et avec 55 % des menuisiers qui travaillaient le bois dur. Les aspirations sur machines fixes existaient seulement dans 28 % versus 3 % sur machines portatives et uniquement 27 % des travailleurs utilisaient des moyens de protection individuels. L’obstruction nasale restait le signe le plus rapporté à 59 %. Conclusion Les scores laissent prévoir un empoussièrement excessif. Les signes irritatifs et allergiques sur le tractus des voies aériennes supérieures ont été observés. Axant nos priorités sur la prévention et la sensibilisation des menuisiers

Optically monitored nuclear spin dynamics in individual GaAs quantum dots grown by droplet epitaxy

We report optical orientation experiments in individual, strain free GaAs quantum dots in AlGaAs grown by droplet epitaxy. Circularly polarized optical excitation yields strong circular polarization of the resulting photoluminescence at 4K. Optical injection of spin polarized electrons into a dot gives rise to dynamical nuclear polarization that considerably changes the exciton Zeeman splitting (Overhauser shift). We show that the created nuclear polarization is bistable and present a direct measurement of the build-up time of the nuclear polarization in a single GaAs dot in the order of one second.Comment: 7 pages, 3 figure

Toksikološke metode otkrivanja opojnih droga u tragovima: kromatografska, spektroskopska i biološka karakterizacija derivata ecstasyja

Analysis often reveals variability in the composition of ecstasy pills from pure 3,4-methylenedioxymethamphetamine (MDMA) to mixtures of MDMA derivatives, amphetamine, and other unidentifi ed substances. For a comprehensive toxicological analysis one needs to know all steps to MDMA synthesis which may originate impurities. The aim of this study was to synthesise and determine the chemical-physical and in vitro biological properties of a series of MDMA derivatives. 3,4-methylendioxyphenyl-2-nitropropene (MDNP) was obtained by condensation of piperonal with an excess of nitroethane in the presence of ammonium acetate. MDNP was then reduced to methylenedioxyamphetamine (MDA) by LiAlH3. All compounds were analysed using HPLC and spectroscopic technique [Raman, nuclear magnetic resonance (NMR), or infrared (IR)] at all the steps of synthesis. In addition, we assessed the biological potentials of these compounds by measuring in vitro their (i) blood cell/whole blood partition coeffi cient, (ii) binding to plasmatic proteins (Fbp), and (iii) membrane adsorption. Chemical structure was determined with antibody fl uorescence polarisation immunoassay (FPIA). This study showed the presence of solid impurities, particularly of a neurotoxic compound of Al3+ in the fi nal products. FPIA identifi ed the aminoethane group close to the substituted benzene ring, but did not detect the two major precursors of MDMA: MDNP and piperonal. Raman spectroscopy is an attractive alternative technique to characterise ecstasy pills and it can identify stereoisomeric forms such as cis-MDNP and trans-MDNP, which exhibit signals at 1650 cm-1 and 1300 cm-1, respectively.Analize često otkriju neujednačenost sastava tableta ecstasyja od čistoga 3,4-metilendioksimetamfetamina (MDMA) do mješavina njegovih derivata, amfetamina i drugih neutvrđenih tvari. Stoga je za kvalitetnu toksikološku analizu potreban uvid u sve korake sinteze MDMA, s obzirom na to da se ondje vjerojatno kriju izvori nečistoće (prekursori, katalizatori). Cilj ovog ispitivanja bio je sintetizirati derivate MDMA te napraviti njihovu kemijsko-fi zikalnu i biološku in vitro karakterizaciju. 3,4-metilendioksifenil-2-nitropropen (MDNP) dobiven je kondenzacijom piperonala u suvišku nitroetana uz dodatak amonijeva acetata. Njegovom redukcijom s pomoću LiAlH3 dobiven je 3,4-metilendioksiamfetamin (MDA). Svi spojevi iz pojedinih koraka sinteze karakterizirani su s pomoću tekućinske kromatografi je visoke djelotvornosti (HPLC) i spektroskopskih tehnika [Ramanove spektroskopije, nuklearne magnetske rezonancije (NMR-a) te infracrvene spektroskopije (IR-a)]. Usto je ocijenjen i njihov biološki učinak in vitro mjerenjem (i) koefi cijenta raspodjele krvna stanica/puna krv, (ii) vezanja za bjelančevine u plazmi (Fbp) te (iii) adsorpcije na membranu. Kemijska je struktura utvrđena s pomoću fl uorescentnoga polarizacijskog imunokemijskog testa (FPIA). Analiza je u konačnim proizvodima utvrdila prisutnost krutih nečistoća, napose spojeva neurotoksičnog aluminija (Al3+). FPIA je prepoznao aminoetansku skupinu blizu supstituiranoga benzenskog prstena, ali ne i dva glavna prekursora za MDMA: MDNP i piperonal. Posebno je zanimljiva Ramanova spektroskopija budući da (i) pruža privlačnu alternativu za karakterizaciju sastava tableta ecstasyja te (ii) može otkriti stereoizomerne cis/trans-oblike spoja poput cis-MDNP-a odnosno trans-MDNP-a, čiji se signal vidi na 1650 cm-1 odnosno 1300 cm-1

Quantitative imaging of dielectric permittivity and tunability with a near-field scanning microwave microscope

We describe the use of a near-field scanning microwave microscope to image the permittivity and tunability of bulk and thin film dielectric samples on a length scale of about 1 micron. The microscope is sensitive to the linear permittivity, as well as to nonlinear dielectric terms, which can be measured as a function of an applied electric field. We introduce a versatile finite element model for the system, which allows quantitative results to be obtained. We demonstrate use of the microscope at 7.2 GHz with a 370 nm thick barium strontium titanate thin film on a lanthanum aluminate substrate. This technique is nondestructive and has broadband (0.1-50 GHz) capability. The sensitivity of the microscope to changes in relative permittivity is 2 at permittivity = 500, while the nonlinear dielectric tunability sensitivity is 10^-3 cm/kV.Comment: 12 pages, 10 figures, to be published in Rev. Sci. Instrum., July, 200

Impact of heavy hole-light hole coupling on optical selection rules in GaAs quantum dots

We report strong heavy hole-light mixing in GaAs quantum dots grown by droplet epitaxy. Using the neutral and charged exciton emission as a monitor we observe the direct consequence of quantum dot symmetry reduction in this strain free system. By fitting the polar diagram of the emission with simple analytical expressions obtained from k$\cdot$p theory we are able to extract the mixing that arises from the heavy-light hole coupling due to the geometrical asymmetry of the quantum dot.Comment: 4 pages, 2 figure

Analytical Models Synthesis of Power Electronic Converters

In this paper we proposes a synthesis of different mathematical models of power electronic converters based on Thevenin/Norton equivalent circuits. Those models, composed by impedances and harmonic noise sources, are helpful to predict the conducted ElectroMagnetic Interferences (EMI) generated by converters connected to the electrical network. Moreover, the extracted impedances are determining for sizing EMC filters. The proposed analytical model is tested with PSpice simulations and validated by experimental measurements, from DC frequency until 30MHz